The present invention relates to biomedical implants, and more particularly to an implantable telemetry sensor for monitoring bone fracture fixation devices.
Historically, radiography has been used to monitor fracture healing. This method gives only qualitative indications of the extent of healing and cannot be used for continuous everyday monitoring. Monitoring has also been performed with strain gauges used to make regular measurements in orthopedic implants so as to assess the quantitative characterization of the healing process. These efforts are directed towards reducing the number of mechanical implant failures and bone refracturing events. However, the powering of strain sensors has been a major obstacle. They have been powered by percutaneous leads that are potential infection sites, battery power which is dependent on battery longevity, and inductive powering which either complicates surgical procedures and/or requires large external power supplies. These methods are only suited for short-term laboratory testing and are impractical for long-term clinical use. Moreover, prior art sensors required relatively high power requirements and used from 500 mW of battery power to 5 watts of induced external power.
It would be desirable to provide a fracture healing assessment technique that is inexpensive and gives qualitative indications of the extent of healing. It would also be desirable to allow for monitoring of dangerous overloads during rehabilitation exercises or day-to-day living. Additionally, a desired device should be non-intrusive and compatible with existing surgical techniques.